The present invention relates to systems for imaging three-dimensional surfaces, and in particular, it concerns methods and systems for deriving depth information from variations in intensity when an object scene is illuminated by different light sources.
It is known to use various techniques to produce three-dimensional images, i.e., images containing information about the subject scene in three-dimensions. Three-dimensional imaging is of particular importance in the field of computerized imaging for sensing object shape, especially in artificial intelligence applications such as robotic object sorting, and in product dimensional inspection.
Conventional three-dimensional imaging techniques are of three main types: stereoscopic imaging in which depth is derived from parallax by identifying corresponding features in two different views of an image; optical radar techniques based on time-of-flight of reflected light; and patterned light illumination. These techniques are all well known for those familiar with the art and will not be described here in detail. An overview of the state of art as it is known to the inventor may be found in "Optics, Illumination, and Image Sensing for Machine Vision VIII" SPIE Proceedings Vol. 2065, September 1993!, which is hereby incorporated in its entirety as if fully set out herein.
Each of the conventional techniques suffers from serious shortcomings. Stereoscopic imaging presents problems of correlation between features of the two images, particularly in cases of smooth featureless surfaces. Optical radar and patterned light illumination, on the other hand, require highly complex hardware or are limited to sensing coarse features of the subject.
There is therefore a need for a simple yet effective method and system for deriving depth information relating to points in an image, in particular, for small objects and close ranges.